gastrointestinal secretions Flashcards
what is gastric acid secreted by ?
parietal cells found in the gastric glands - secrete HCl
what is the stomach protected by ?
mucous and bicarb secreted by neck cells
what are the stimuli for the secretion of gastric acid in the stomach ?
gastrin - binds to CCKB on parietal cells
gastrin - activates ECl cells to release histamine to stimulate parietal cells
vagus nerve - release Ach to bind to M3 receptors on parietal cells
as well as activation of G cells by GRP
blocking the vagus wont stop acid secretion
what are the drugs used to decrease acid secretion ?
atropine - muscarinic blocker
why doesn’t atropine work very well in order to suppress acid ?
because atropine is a muscarinic blocker
doesn’t stop the stimulation by the vagus nerve onto G cells
where does intrinsic factor come from and what does it do ?
from parietal cells , used for vitamin b12 uptake
what is the physiology of the parietal cells ?
2 seperate pumps where one is an ATPase pump that pumps out hydrogen for potassium
and another that secretes chlorine
what are the hydrogen ions formed by the parietal cells synthetised by ?
carbonic nhydrase enzyme
what is the alkaline tide ?
an increase of bicarb that comes with an increase in H+ production
why does vomiting cause metabolic alkalosis ?
when Hcl is vomited
there is an increase in H+ secretion and hence the bicarb production
urine chloride is low
what is the purpose of measuring urinary chlorine levels and what do the different results indicate ?
useful for patients with metabolic alkalosis with an unknown cause
low ? vomiting is the cause
high ? diuretics
what are the different receptors on parietal cells and what are they stimulated by ?
M3 - Ach
CCKb - Gs
H2- histamine
all of these directly stimulate the AtPase
what are the two naturally occurring substances that can inhibit the stimulation of the parietal cells ?
somatostatin
prostaglandin
what are the second messengers for each of the substances stimulating the parietal cells ?
1- Ach and gastrin both work via Gq proteins with IP3/Ca
2- Somatostatin, histamine, PGs work via Gs/i and cAMP
what is the source of somatostatin ?
D cells
where are chief cells found and what do they do ?
found in the gastric glands , they secrete pepsin
what is the stimulus of release for pepsin ?
vagus stimulation
what is the best pH for pepsin ?
low acidic
